Revert "Use native async/await support in pub."

sdk/lib/_internal/pub_generated/test/build/utils.dart

+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:convert';
+
+import '../descriptor.dart' as d;
+import '../test_pub.dart';
+
+/// Runs the hosted test server and serves a valid "browser" package that
+/// contains the same files (but not their contents) as the real browser
+/// package.
+void serveBrowserPackage() {
+  serve([d.dir('api', [d.dir('packages', [d.file('browser', JSON.encode({
+          'versions': [packageVersionApiMap(packageMap('browser', '1.0.0'))]
+        })),
+            d.dir(
+                'browser',
+                [
+                    d.dir(
+                        'versions',
+                        [
+                            d.file(
+                                '1.0.0',
+                                JSON.encode(
+                                    packageVersionApiMap(packageMap('browser', '1.0.0'), full: true)))])])])]),
+            d.dir(
+                'packages',
+                [
+                    d.dir(
+                        'browser',
+                        [
+                            d.dir(
+                                'versions',
+                                [
+                                    d.tar(
+                                        '1.0.0.tar.gz',
+                                        [
+                                            d.file('pubspec.yaml', yaml(packageMap("browser", "1.0.0"))),
+                                            d.dir(
+                                                'lib',
+                                                [
+                                                    d.file('dart.js', 'contents of dart.js'),
+                                                    d.file('interop.js', 'contents of interop.js')])])])])])]);
+}